Ring-to-Cage Structural Conversion via Template Effect in a Gold(I) Metallosupramolecular System

A unique example of a ring-to-cage structural conversion in a multinuclear gold(I) coordination system with d-penicillamine (d-H₂ pen) is reported. The reaction of [Au₂ Cl₂ (dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) with d-H₂ pen in a 1:1 ratio gave [Au₄ (dppe)₂ (d-pen)₂ ] ([1]), in which two [Au₂ (dppe)]²⁺ units are linked by two d-pen S atoms in a cyclic form so as to have two bidentate-N,O coordination arms. The subsequent reaction of [1] with Cu(OTf)₂ afforded [Au₄ Cu(dppe)₂ (d-pen)₂ ]²⁺ ([2]²⁺ ), in which a Cu^II ion is chelated by the two coordination arms in [1] to form an Au^I₄ Cu^II bicyclic metallocage. A similar reaction using Cu(NO₃ )₂ was accompanied by the ring expansion of [1] to [Au₈ (dppe)₄ (d-pen)₄ ], leading to the production of [Au₈ Cu₂ (dppe)₄ (d-pen)₄ ]⁴⁺ ([3]⁴⁺ ). In [3]⁴⁺ , two Cu^II ions are each chelated by the two coordination arms to form an Au^I₈ Cu^II₂ tricyclic metallocage, accommodating a nitrate ion. The use of Ni(NO₃ )₂ or Ni(OAc)₂ instead of Cu(NO₃ )₂ commonly gave a tricyclic metallocage of [Au₈ Ni₂ (dppe)₄ (d-pen)₄ ]⁴⁺ ([4]⁴⁺ ), but a water molecule was accommodated inside the Au^I₈ Ni^II₂ metallocage.